Direct resistance heating electrical furnaces of various types have been proposed in which electrical current is passed between two spaced electrodes having a bed of conductive particulate material therebetween. The resistance of the bed causes it to heat and thereby give rise to some form of chemical or physical change in the material or other sub-divided, solid or gaseous materials admixed therewith.
As far as applicant is aware, the control of such furnaces is generally achieved either empirically by an operator or by measuring the temperature of the bed of particulate material at one or more predetermined positions within the furnace. The residence time of the material in the furnace at a predetermined temperature determines the extent of the chemical or physical change and thus the quality of the product.
The disadvantage of utilising temperature measurements, for example by means of one or more thermocouples at one or more specific locations within the furnace, is that the measurement may be inaccurate by reason of prevailing hot or cold spots at such location or locations. Also, where thermocouples are employed, their life is generally limited and often the operation of a furnace is interrupted when a thermocouple ceases to function correctly. These factors, in turn, lead to supervision being required and also to repair and replacement of components, in particular thermocouples, being necessary from time to time.
Furthermore, such furnaces often have an outlet valve at the bottom of the furnace which can have a deleterious effect on certain particulate materials being treated therein, for example granular activated carbon which is being reactivated.
It is the object of this invention to provide a direct resistance heating electrical furnace assembly and method of operating same in which the aforementioned disadvantages may, at least to some extent, be alleviated.